This application claims priority to Korean Patent Application No. 2004-35371, filed on May 18, 2004, in the Korean Intellectual Property Office, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a method for processing a call in a mobile communication terminal supporting a multi-mode telecommunication system and, more particularly, to a method for processing a call when the mobile communication terminal receives a call release order in a specific mode.
2. Description of Related Art
A tri-mode communication system enables an automatic switching operation among three systems, i.e., Personal Communication Service (PCS), Code Division Multiple Access (CDMA), and Advanced Mobile Phone Service (AMPS), and provides seamless communications in a region where these systems coexist. The term “multi-mode”, or “multi-mode telecommunication system” as used in this specification refers to a complex system supporting a plurality of different mobile communication systems.
A mobile communication terminal supporting the tri-mode usually enters into a system determination state when it receives a call release order from the AMPS system. That gives the terminal a chance to scan the systems through a system reselection process and to select the CDMA system since the CDMA system is more advantageous than the AMPS system in most cases.
The mobile communication terminal supporting the tri-mode is equipped with a system determination algorithm for controlling a switching operation among these systems. For example, Qualcomm's MSM 6000 series chipsets are provided with an SD 2.0 algorithm. The SD 2.0 algorithm supports script resources provided in the form of an object to be independently called and used as needed. When a mobile communication terminal using the SD 2.0 algorithm receives a call release order while operating in the AMPS system, it enters into an analog idle state by way of an analog init state, and exits into the system determination state if a 4 sec timer expires. A chance to switch to an optimum system is obtained by scanning multiple systems in the system determination state.
Meanwhile, a typical AMPS system utilizes a call setup process as shown in FIG. 3. First, when a base station transmits a page order to a mobile station (step S201), the mobile station transmits a page response message in response to the page order and waits for the base station to designate a voice channel (step S203). Subsequently, when the mobile station receives a voice channel designate message from the base station, it tunes itself to a designated channel (step S205). Next, the base station transmits an ‘Alert With Info’ message, and the mobile station rings a bell upon receipt of the message (step S207). When a user pushes keys, the mobile station transmits a connect order to the base station (step S209), and then a conversation state is established (step S211).
However, another AMPS system in a specific region has a call processing process different from the above-mentioned AMPS system. FIG. 4 shows another call setup process of the AMPS system utilized in such a region. First, a base station transmits a page order to a mobile station (step S301). The mobile station transmits a page response message in response to the page order, and waits for the base station to designate a voice channel (step S303). Unlike the case of FIG. 3, the base station does not transmit a voice channel designate message but instead transmits a release order requesting a call release (step S305). Subsequently, the base station transmits the page order once again to the mobile station a few seconds later (step S201), and the above-mentioned process shown in FIG. 3 follows. What the base station issues a call release order with respect to the first page response message of the mobile station seems to be part of a call re-establishment process in the AMPS system.
In such a region, a mobile station equipped with Qualcomm's SD 2.0 algorithm may have a serious problem as follows. That is, in the step S201 where the base station transmits the page order for a call setup for the second time after the step S305 where the release order is received, the mobile station may recognize the received release order as an instruction to perform a call release and enter into a system re-determination state. Since the call release order is made during the call setup process in such a region, the mobile station equipped with the SD 2.0 algorithm may fail to perform the call setup at this time. That is, it may be not possible for the mobile station to receive a call in such a region.